Field of the Invention
The present invention relates to the joining of pipes and specifically to a seal for sealing a space connecting a belled end of a length of pipe to the spigot end of a length of pipe or fitting and methods for manufacturing the same. The seal is an improved seal that includes two different materials which can be used in a Rieber type belling process to interconnect the belled and spigot pipes. More specifically, the present invention discloses an improved seal exhibiting an improved cross sectional profile established between a first material such as rubber or other material and a second material such as a plastic polymer. The forming process further establishes high bond line strength between the first and second materials.
Description of the Related Art
Pipelines for conveying fluids can be made from a number of different materials, including plastic materials, such as polyethylene or polyvinyl chloride (PVC), and metals, such as steel, brass and aluminum. Pipes formed from plastic materials are used in a variety of industries. Each length of such pipe typically has a belled female end and a spigot male end. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. The joints between sections of pipe are sealed, typically with a gasket. For example, an annular, elastomeric ring or gasket is typically seated within a groove formed in the belled end of the pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint.
Prior art examples of reinforced rubber seals are interposed between interconnecting end to end connected sections of pipe fittings and the like. For example, a system was developed for connecting sections of PVC pipe and for connecting fittings to PVC pipe. These PVC pipe systems have relied mainly on the “Rieber Joint,” which was developed in the early 1970's by Rieber & Son of Bergen, Norway, to seal the connections (see for example U.S. Pat. No. 4,368,894 to Parmann). The Rieber seal was developed in order to address certain problems, including preventing the dislodgement of a homogeneous and non-reinforced elastomeric seal from an associated inner annular bell groove during insertion into the bell of an engaging spigot end of a succeeding pipe section.
The Rieber joint has an elastomeric gasket inserted into a groove on the inside of the belled end of a piece of the PVC pipe as the female end is being formed. Conventional Rieber seals used in a Rieber joint include a steel wire or flattened band which is either externally or internally bonded. The steel wire or band is disposed proximate to the exterior perimeter of the annular extending elastomer body and is locked into place within the bell groove due to pre-stressing of the elastomer against the inner annular wall of the pipe. The seal prevents the penetration of soil and other foreign particles into a sealing zone established between the outer walls of the seal and the internal walls of the bell where the seal is seated. In this fashion, the steel ring operates to hold open the seal for subsequent inter-assembly and during the initial belling process. External elements are then added to restrain the pipe after the joint is assembled.
The seal described above is loaded on an outer surface of a substantially cylindrical forming mandrel. An end portion of a thermoplastic material pipe is in a heated, softened state when it is pushed over the mandrel. The seal is located on the mandrel. Thereby, the female pipe end portion is formed into a socket, in which the seal forms a groove in the socket. An outer surface of the seal molds the female pipe end portion in a belled shape as the female pipe is pushed over the seal. The seal is retained in the groove. After cooling, the pipe and the seal are withdrawn from the mandrel with the seal remaining in the groove formed in the socket end. When jointing the pipe with another pipe the seal is used for sealing the space between the socket end and the spigot end of a pipe introduced into the socket end.
The seal functions as a forming element during fabrication. Once assembled between interconnected pipes, the seal functions as a sealing element. To be able to comply with its purpose as a forming element the seal needs to resist forces exerted on the seal during the forming operation. To this end, the seal includes a rigid metal ring. To comply with the sealing function, the seal has elastomeric features. In order to achieve these requirements, the Rieber seal includes a first annular sealing portion consisting of elastically yieldable sealing material with an embedded annular portion for reinforcing the seal. For the Rieber seal, the reinforcing portion consists of a steel ring which is enclosed in the elastically yieldable material of the annular sealing portion. In a seal of this kind the elastically yieldable material is utilized not only for providing the sealing function but also as the forming portion of the seal by the fact that the major portion of the external surfaces of the seal, i.e. the surfaces engaging the forming mandrel as well as the surfaces engaged by the softened thermoplastic material during the forming operation, are the elastically yieldable sealing material.
The Rieber Joint has several disadvantages, including the possibility of failure due to the complexity of the combined steel wire or flattened band and seal. Further, the steel wire or flattened band may become exposed to the elements during its lifetime resulting in corrosion of the wire or band. This exposure of the wire or band can occur if the seal is damaged during installation or pipe assembly. In certain cases, prolonged use results in the outer rubber material locally cracking to expose the wire or band. It is also critical, during the installation process, that the Rieber seal not twist or flip since a displaced or dislocated seal will adversely affect the ultimate sealing capacity of the joint. It is also critical to the success of the pipe joint that the seal be maintained in the proper position in its respective groove during installation and use. For large diameter pipes, the insertion force needed to install the male spigot end within the mating socket end and seal requires a high insertion force which could, on some occasions, cause the gasket to be distorted or displaced.
Thus, a need exists for a seal for bell and spigot pipes and fittings that provides ease of assembly during the forming process without the risk of corrosion while still maintaining the integrity of the seal. A further drawback of the seal of the prior art type is that the steel rings constituting the reinforcing portions of the seal are relatively expensive. The object of the present invention is to provide an improved seal in the respects discussed above.